1. Field of the Invention
The invention relates to a method for transmitting useful information in a radio communication system with at least one radio network control device, at least one base station and at least one user station.
2. Description of the Related Art
Communication systems are becoming increasingly important in both the economic and private spheres. Serious efforts are being made to link cable-based communication systems to radio communication systems. The resulting hybrid communication systems increase the number of available services and also allow greater flexibility in respect of communication. Devices are therefore being developed that can use different systems (multi-homing).
Radio communication systems are increasing in importance because of the mobility they allow users.
In radio communication systems information (e.g. voice, image information, video information, SMS [Short Message Service] and other data) is transmitted using electromagnetic waves via a radio interface between the sending and receiving stations (base station and user station). The electromagnetic waves are thereby emitted at carrier frequencies in the frequency band provided for the respective system.
Frequencies of 900, 1800 and 1900 MHz are used for the existing GSM mobile radio system (Global System for Mobile Communication). These systems essentially transmit voice, telefax and SMS (Short Message Service) as well as digital data.
Frequencies in the frequency band of approx. 2000 MHz are provided for future mobile radio systems with CDMA or TD/CDMA transmission methods, such as UMTS (Universal Mobile Telecommunication System) or other third generation systems. These third generation systems are being developed with the objectives of worldwide radio coverage, a wide range of services for data transmission and most importantly flexible management of the capacity of the radio interface, which is the interface with the fewest resources in radio communication systems. With these radio communication systems it should be possible for a user station to be able to send and/or receive a large quantity of data if required at a high data speed, primarily through flexible management of the radio interface.
Access by the stations to common radio resources of the transmission medium, e.g. time, frequency, output or space, is regulated in these radio communication systems by Multiple Access (MA) methods.
In the case of Time Division Multiple Access (TDMA) methods, each send and receive frequency band is divided into time slots, with one or several cyclically repeated time slots being allocated to the stations. TDMA separates the radio resource time in a station-specific manner.
In the case of Frequency Division Multiple Access (FDMA) methods, the overall frequency range is divided into narrow-band domains, with one or several narrow-band frequency bands being allocated to the stations. FDMA separates the radio resource frequency in a station-specific manner.
In the case of Code Division Multiple Access (CDMA) methods, a spread code using a large number of individual so-called chips is used to code the output/information to be transmitted in a station-specific manner, as a result of which the output to be transmitted is spread in a random manner based on the code over a large frequency range. The spread codes used by different stations within a cell/base station are orthogonal or essentially orthogonal in respect of each other in each instance, so the receiver identifies the signal output intended for it and suppresses other signals. CDMA separates the radio resource output in a station-specific manner using spread codes.
In the case of Orthogonal Frequency Division Multiplexing (OFDM) methods, the data undergoes broadband transmission with the frequency band divided into equidistant, orthogonal subcarriers, so that the simultaneous phase shift of the subcarriers generates a two-dimensional data flow in the time-frequency domain. OFDM separates the radio resource frequency in a station-specific manner using orthogonal subcarriers. The combined data symbols transmitted during a time unit on the orthogonal subcarriers are referred to as OFDM symbols.
Multiple access methods can be combined. Many radio communication systems therefore use a combination of the TDMA and FDMA methods, with each narrow-band frequency band divided into time slots.
For the UMTS mobile radio system referred to a distinction is made between a so-called FDD (Frequency Division Duplex) mode and a TDD (Time Division Duplex) mode. The TDD mode is characterized in particular in that a common frequency band is used both for signal transmission in the uplink UL and the downlink DL, while FDD mode uses a different frequency band for each of the two transmission directions.
In second and/or third generation radio communication connections information can be transmitted circuit switched CS or packet switched PS.
The connection between the at least one base station and the at least one user station is established via a radio communication interface. The at least one base station and radio network control device are components of a base station subsystem (RNS Radio Network Subsystem). A radio communication system generally includes several base station subsystems, which are linked to a core network CN. The radio network control device of the base station subsystem is thereby connected to an access device of the core network.
Data made available to several users is transmitted in radio communication systems as well as individual items of useful information. Such useful information includes video streams for example. Useful information, which is made available to several users, is combined under the term MBMS (Multimedia Broadcast/Multicast Service).
It is essentially of major importance for all network resources to be used as sparingly as possible. Efforts are made in particular to ensure that the radio network requires as little information as possible about the respective users, as otherwise a significant quantity of information potentially has to be stored in the radio network.
Radio communication systems interfacing with a core network are therefore known, with the following network nodes having important functions for transmission of the services:                the access device to the core network (SGSN Serving GPRS Support Node), which holds both service-specific and user-specific information,        the radio network control device (RNC Radio Network Controller), which holds service-specific information.        